The mammary gland is commonly referred to as the breast and is a unique feature of mammals who suckle their infants after birth.

Normal structure of the breasts

Mammary glands or breasts are actually sweat glands that have been modified according to hormonal stimulation. Male and female breasts are different due to the different hormonal stimulation that occurs with each gender. The presence of the female hormone estrogen is responsible for the growth and development of the female breasts. In most males, the glandular tissue within the breast remains rudimentary.
 

The breast tissues comprises ducts or tubes that carry milk into the nipple. In females, there are fine branching ductules or smaller tubules that lead to the nipple where the tips of the ducts meet. At the ends of the ducts are the milk secreting alveoli. The ducts and the glandular tissues are surrounded by connective tissue called stroma aswell as fatty or adipose tissue. This nipple is surrounded by a darker pigmented circular area called the areola.

As a girl reaches puberty, the mammary gland continues to grow during every menstrual cycle. When the levels of estrogen are high, the ducts proliferate or multiply until full growth is achieved.

Hormonal regulation of the breasts

Development of the female breast is dependent on female hormones estrogen, growth hormone and prolactin. Estrogen regulates the development of the breast ducts. When a woman is pregnant, the hormones estrogen, progesterone and prolactin cause proliferation of the lobules and ducts within the breast. While estrogen leads to proliferation of the ducts, progesterone helps in the development of the alveoli, lobule and ductal branching and ductal enlargement. Prolactin stimulates lactogenesis or milk production to provide food for the baby after birth.

Age related changes in the mammary glands

In females, the mammary glands start to grow with each menstraul cycle throughout puberty until they are fully developed. Further growth occurs during pregnancy, after giving birth and during breast feeding. During the menopause, the estrogen declines leading to shrinkage of the breasts and a certain amount of reduction in their size.